Vibration isolation and sound isolation systems are well known in the art. These systems utilize microprocessors to supply canceling waves to cancel or minimize vibration or sound within a defined area. The canceling waves are generally responsive to an external input signal(s). Examples of such systems are taught in U.S. Pat. Nos. 4,677,676 to Eriksson, 4,153,815 to Chaplin, 4,122,303 to Chaplin et al., 4,417,098 to Chaplin et al., 4,232,381 to Rennick et al., 4,562,589 to Warnaka et al., 4,473,906 to Warnaka et al., 4,878,188 to Zeigler, Jr., 5,170,433 to Elliott, 5,133,527 to Chen et al., and 4,689,821 to Salikudden et al., the disclosures of each which are hereby incorporated by reference herein. In these systems, the control scheme that is used can be least mean square (LMS), Filtered-X LMS, or the like.
Some active control systems utilize adaptive feedforward control. These systems operate on the input disturbance to generate a cancellation force. Such systems in the prior art utilize a Digital Signal Processor (DSP) as the CPU to implement the feedforward path, i.e., processing of the input signal and also for implementing the adaptation path, i.e., calculating the adaptation weight coefficients. Notably, because the same DSP is used to perform the calculations for the feedforward and adaptive paths simultaneously, the computational burden is immense in these prior art systems.
The feedforward path generally requires a high data flow rate because it is filtering the input waveform to produce output signal(s) or canceling waves to an output transducer (speaker or actuator). In general, the data flow rate must be many times higher than the highest frequency to be controlled. On the other hand, the adaptation path does not require the same high data flow rate. In fact, the adaptation path may be shut down temporarily whereas the feedforward path may never be. Therefore, there is a need for a system that will implement the feedforward path and the adaptation path, yet will economize on the DSP's computational load.